1. Field of the Invention:
The present invention relates to a double action die set in a closed forging press.
2. Description of the Prior Art:
One example of a double action die set in a closed forging press in the prior art is illustrated in FIGS. 4 to 6. FIG. 4 shows an opened state of a die set before pressing, FIG. 5 show the state when pressing has completed, and FIG. 6 is a cross-section view showing an opened state of a die set after pressing. With reference to these figures, in a press consisting of a stationary base 1 and a slide 2 that is reciprocated by crank action or the like, a double action die set in the prior art is composed of a stationary side die 5 fixedly provided on the stationary base 1 and provided with an oil chamber 3, a piston 4 supported by a hydraulic pressure in the oil chamber 3, and a knock-out piston 43 slidably engaged with a rod portion of the piston 4 therein, a movable side die 10 fixedly provided on the slide 2 and provided with an oil chamber 6, a piston 7 supported by a hydraulic pressure in the oil chamber 6, an oil chamber 8 and a piston 9 supported by a hydraulic pressure in the oil chamber 8 therein, an outer metal mold 51, an inner metal mold 44, a metal mold 12, and punches 13 and 14. On a main body surface 15 of the stationary side die 5 is fixedly provided the outer metal mold 51, the inner metal mold 44 slidably fitted to the inner diameter portion of the outer metal mold 51 is also supported on the main body surface 15, the inner metal mold 44 is supported by the knock-out piston 43, the punch 13 is fixedly secured to the piston 4, the metal mold 12 is fixedly secured to the piston 7 of the movable side die 10, and the punch 14 is fixedly secured to the piston 9.
To the pistons 4 and 9 are respectively connected oil paths of pull-back hydraulic pressures 16 and 17, and the oil chambers 3, 6 and 8 are all connected through one closed hydraulic circuit 18. To this hydraulic circuit 18 is connected a hydraulic pressure generator normally through a check valve 19, and a pressure relief valve 21 is equipped to the hydraulic circuit 18. An oil chamber 46 on the opposite side of the knock-out piston 43 to the piston 4 is connected to a hydraulic pressure device 47 via a switching valve 45.
When a raw material 22 is charged within the outer metal mold 51 and the inner metal mold 44 by means of a forging raw material feeder not shown and the slide 2 is actuated in the closing direction indicated by an arrow P in FIGS. 4 and 5 by means of a drive unit not shown, the outer metal mold 51 and the metal mold 12 would join together, and a closed space 23 is formed. Furthermore, as the actuation of the slide 2 proceeds, the pressurized oil within the oil chamber 6 would move to the oil chambers 3 and 8 via the closed hydraulic circuit 18 as distributed depending upon pressure balance among the respective oil chambers, and would actuate the pistons 4 and 9 in the directions indicated by arrows Q in FIG. 5, so that the raw material 22 is pressed by the punches 13 and 14 to be formed into a shaped product 24.
When the slide 2 is actuated in the opening direction indicated by an arrow R in FIGS. 5 and 6 by means of the aforementioned drive unit not shown, the pistons 4 and 9 are respectively restored to their original positions by the pull-back hydraulic pressures 16 and 17 also the pressurized oil in the oil chambers 3 and 8 would move to the oil chamber 6 via the closed hydraulic circuit 18, in addition the metal mold 12 are separated from the outer metal mold 51, resulting in an opened state, due to removal of a pressure in the oil chamber 46 by means of the switching valve 45, the knock-out piston 43 as well as the inner metal mold and the product 24 supported by the piston 43 would rise, and the product 24 is ejected from the inner metal mold 44 by means of a product ejection device not shown and sent to the next step of the process.
However, the double action die set in the prior art as described above is accompanied by a number of shortcomings as will be enumerated in the following:
(1) Since the movable side die 10 has a two-chamber construction including the oil chambers 6 and 8, it is compelled to serially dispose the piston 7 and the piston 9, hence a height of a die becomes high, and the die cannot be equipped in an existing press.
(2) Due to the fact that during operation a large amount of pressurized oil move within the closed hydraulic circuit 18 in a short period of time, a size of pipings would become extremely large, also an operation speed of the press, that is, a number of strokes per minute has a limit, and so, speed-up cannot be achieved.
(3) Since the amounts of pressurized oil moving to the oil chambers 3 and 8, respectively, are different depending upon pressure balance between the oil chambers 3 and 8, and also since the loads applied to the punches 13 and 14 which correspond to these pressures are generally different, a difference is produced between the amounts of movement of the pistons 4 and 9, and poor precision in the products is liable to occur.
(4) As the knock-out of the product 24 is effected by switching the switching valve 45, a necessary operation time becomes long and speed-up of the operation is limited, consumed energy is large, maintenance is laborious, and an existing knock-out drive unit cannot be used.